A power supply unit includes a switching circuit that drives a switching device by a duty ratio corresponding to a target voltage output value and outputs an alternating current signal; a coupling capacitance element provided in a subsequent stage with respect to the switching circuit; a voltage transformation unit that increases a voltage of the alternating current signal input by using the switching circuit, and outputs a high-voltage alternating current voltage to an electrifying unit; a charging unit that charges the coupling capacitance element in response to a power supply voltage being turned on; and a control unit that controls driving of the switching device to cause the coupling capacitance element to be charged to a predetermined charged amount before the switching circuit starts outputting the alternating current signal.
Legal claims defining the scope of protection. Each claim is shown in both the original legal language and a plain English translation.
1. A power supply unit comprising: a switching circuit that drives a switching device at a duty ratio corresponding to a target voltage output value and outputs an alternating current signal; a coupling capacitance element provided in a subsequent stage with respect to the switching circuit; a voltage transformation unit that increases a voltage of the alternating current signal input by using the switching circuit, and outputs, a high-voltage alternating current voltage to an electrifying unit; a charging unit that charges the coupling capacitance element in response to a power supply voltage being turned on; and a control unit that controls the switching device to cause the coupling capacitance element to be charged to a predetermined charged amount before the switching circuit starts outputting the alternating current signal.
A power supply unit boosts voltage for an electrifying unit (like in a printer) using a switching circuit, a capacitor, and a voltage transformer. The switching circuit uses a switching device controlled by a duty ratio based on a target output voltage and generates an AC signal. A capacitor smooths the output after the switching circuit. The transformer then steps up the voltage to a high-voltage AC suitable for the electrifying unit. Crucially, before the switching circuit even starts, a charging circuit pre-charges the capacitor to a specific level, managed by a control unit, ensuring stable and predictable voltage output.
2. The power supply unit as claimed in claim 1 , wherein the control unit sets, to an ON signal level, a driving signal that controls driving of the switching circuit after a time corresponding to a time constant that is obtained from an electrical capacitance of the coupling capacitance element and resistance values of resistance elements included in the charting unit has elapsed from when charging of the coupling capacitance element is started in response to the power supply voltage being turned on.
The power supply unit described in claim 1 includes a control unit that determines when to activate the switching circuit based on the capacitor's charging state. Specifically, after the power supply turns on and the capacitor begins charging, the control unit waits a certain time before enabling the switching circuit's driving signal (setting it to an ON state). This wait time is calculated based on the capacitor's capacitance and the resistance of the charging circuit's components, effectively using the RC time constant to ensure the capacitor is sufficiently charged before high-voltage generation begins.
3. The power supply unit as claimed in claim 2 , wherein the time corresponding to the time constant is a charging time required for a voltage applied to the coupling capacitance element reaching within an allowable voltage deviation range, or a time obtained from a margin corresponding to a tolerance of the electrical capacitance of the coupling capacitance element being added to the charging time.
For the power supply unit described in claim 2, the charging wait time (based on the RC time constant) is carefully chosen. It represents the time needed for the voltage on the capacitor to reach a level within an acceptable tolerance of its target voltage. Furthermore, this charging time may be increased slightly to account for manufacturing variations in the capacitor's capacitance. This ensures consistent performance even with component tolerances.
4. The power supply unit as claimed in claim 2 , wherein the control unit obtains the time corresponding to the time constant in which a magnitude of an erroneous output depending on a charged state of the coupling capacitance element becomes equal to or less than a breakdown voltage according to Paschen's rule.
In the power supply unit described in claim 2, the time constant is determined to limit unwanted output voltages. The system calculates the time based on Paschen's law, such that any erroneous output voltage caused by the initial charge state of the capacitor is less than the breakdown voltage. This prevents arcing or other voltage breakdown issues in the electrifying unit due to an improperly charged capacitor.
5. The power supply unit as claimed in claim 2 , further comprising an atmospheric pressure sensor, wherein the control unit obtains the time corresponding to the time constant in which a magnitude of an erroneous output depending on a charged state of the coupling capacitance element becomes equal to or less than a breakdown voltage corresponding to an atmospheric pressure sensor according to Paschen's rule.
The power supply unit described in claim 2 also contains an atmospheric pressure sensor. The control unit adjusts the capacitor pre-charge timing (the time constant) based on the atmospheric pressure. Using Paschen's law, the time is calculated to ensure that any erroneous output voltage due to the capacitor's charged state is below the breakdown voltage for the *current* atmospheric pressure detected by the sensor. This adapts the pre-charge to environmental conditions.
6. The power supply unit as claimed in claim 1 , wherein the coupling capacitance element is charged by a voltage obtained from the power supply voltage being divided according to resistance values of resistance elements included in the charging unit.
In the power supply unit described in claim 1, the capacitor is charged directly from the power supply voltage. However, instead of directly connecting the capacitor to the power supply, the charging circuit uses a voltage divider consisting of resistors. The capacitor is charged by the voltage resulting from the division of the power supply voltage via these resistors, allowing finer control of the pre-charge level.
7. The power supply unit as claimed in claim 1 , wherein resistance values of resistance elements included in the charging unit are a combination of resistance values corresponding to a duty ratio in a case where the target voltage output value is zero, and the resistance values of the resistance elements and an electrical capacitance of the coupling capacitance element have values corresponding to a time from the power supply voltage being turned on to the driving of the switching device being started.
For the power supply unit described in claim 1, the resistors in the charging circuit are chosen carefully. Their resistance values correspond to the duty ratio when the target output voltage is zero. Also, the resistance and capacitance values are selected to create a charging time that matches the time between the power supply turning on and the switching circuit starting. This coordinates the initial charging with the overall power-up sequence.
8. The power supply unit as claimed in claim 2 , wherein the time corresponding to the time constant is previously calculated and stored in a storage device.
In the power supply unit described in claim 2, the charging time (corresponding to the RC time constant) isn't calculated on the fly. Instead, it's pre-calculated and stored in a memory device. The control unit simply retrieves this pre-calculated value, eliminating the need for real-time calculations and potentially simplifying the control unit's design.
9. The power supply unit as claimed in claim 1 , wherein the charging unit includes a first resistance element connected between a terminal of the power supply voltage and one end of the coupling capacitance element, and a second resistance element connected between the end of the coupling capacitance element and a ground point.
The charging circuit in the power supply unit of claim 1 is implemented using a simple two-resistor network. The first resistor connects between the power supply voltage terminal and one side of the coupling capacitor. The second resistor connects between that same side of the coupling capacitor and the ground. This forms a voltage divider to control the initial charge on the capacitor.
10. An image forming apparatus, comprising: the power supply unit claimed in claim 1 ; and the electrifying unit that receives the high-voltage alternating current voltage that is output by the power supply unit, and electrifies a photosensitive member, the photosensitive member being then exposed by signal light and an electrostatic latent image being formed on the photosensitive member.
An image forming apparatus (like a printer) includes both the power supply unit from claim 1 and an electrifying unit. The electrifying unit receives the high-voltage AC output from the power supply. It then uses this voltage to charge a photosensitive drum. After charging, the drum is exposed to light, creating an electrostatic latent image, which is then developed and transferred to paper.
11. A power supply control method, carried out by a power supply unit that includes a switching circuit, a coupling capacitance element provided in a subsequent stage with respect to the switching circuit, a voltage transformation unit to which an alternating current signal is input by the switching circuit, a charging unit connected to the coupling capacitance element, and a control unit, the power supply control method comprising the steps of: the charging unit charging the coupling capacitance element in response to a power supply voltage being turned on; the control unit controlling the switching circuit to cause the coupling capacitance element to be charged to a predetermined charged amount before the switching circuit starts outputting the alternating current signal; the switching circuit driving a switching device at a duty ratio corresponding to a target voltage output value and outputting the alternating current signal; and the voltage transformation unit increasing the alternating current signal that is input by using the coupling capacitance element, and outputting a high-voltage alternating current voltage to an electrifying unit.
This describes a method for controlling a power supply unit that uses a switching circuit, a capacitor, and a voltage transformer. The method involves the charging unit pre-charging the coupling capacitor when power is turned on. The control unit then ensures the capacitor reaches a specific charge level *before* the switching circuit begins operation. After pre-charging, the switching circuit drives a switching device at a duty ratio for the target voltage to generate an AC signal, which the voltage transformer boosts to a high voltage for an electrifying unit.
12. The power supply control method as claimed in claim 11 , wherein in the step of the control unit controlling the switching circuit, the control unit sets, to an ON signal level, a driving signal that controls driving of the switching circuit after a time corresponding to a time constant that is obtained from an electrical capacitance of the coupling capacitance element and resistance values of resistance elements included in the charging unit has elapsed from when charging of the coupling capacitance element is started in response to the power supply voltage being turned on.
The power supply control method described in claim 11 includes a step where the control unit waits a calculated time before activating the switching circuit. This wait time corresponds to the RC time constant of the capacitor and the charging circuit's resistors. The control unit enables the switching circuit's driving signal only *after* this time has elapsed from when the capacitor charging began, ensuring it is properly pre-charged.
13. The power supply control method as claimed in claim 11 , wherein in the step of the control unit controlling the switching circuit, the control unit obtains the time corresponding to the time constant in which a magnitude of an erroneous output depending on a charged state of the coupling capacitance element becomes equal to or less than a breakdown voltage according to Paschen's rule.
The power supply control method described in claim 11 determines the capacitor pre-charge timing based on Paschen's law. The control unit calculates a time (the RC time constant) to ensure that any erroneous output voltage resulting from the initial capacitor charge is less than the breakdown voltage. This prevents unwanted voltage discharge or arcing in the high-voltage system.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
November 24, 2010
July 23, 2013
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